McCain’s e-mail this week takes aim at congressional Democrats, though it avoids criticism of President Obama.

(CNN) - John McCain officially announced a 2010 campaign to hold on to his Senate seat Tuesday, sending supporters a fundraising message asking for help with “a tough re-election challenge.”

McCain won his home state of Arizona by 9 points in November, but the state has become increasingly competitive. Until the state’s Democratic governor, Janet Napolitano, was selected by President Obama to head the Department of Homeland Security, political observers had considered her to a formidable potential challenger to the four-term incumbent.

McCain’s e-mail this week takes aim at congressional Democrats, though it avoids criticism of President Obama.

“While the leader of the Democratic Party, President Obama, has pledged to change business as usual in Washington and spoken of bipartisanship, I have been saddened to watch as Congressional Democrats try to use their majority to advocate more of the same failed policies and wasteful spending of the past,” he writes. “With so much at stake, now is not the time to step away from my work in the Senate.

Following his presidential run, the Republican senator said he intended to seek re-election in 2010 and set up a political action committee as a first step in that process, but the e-mail marks McCain’s official announcement and fundraising pitch to supporters that he plans to defend his Senate seat.